/Engine/Plugins/Media/MediaIOFramework/Source/MediaIOCore/Public/MediaIOCoreTextureSampleBase.h
Set the sample buffer with half it's original height and take only the odd or even line.
bool SetBufferWithEvenOddLine ( bool bUseEvenLine, const void * InVideoBuffer, uint32 InBufferSize, uint32 InStride, uint32 InHeight )